package cpdetector;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class CharSetDetector {
	public static String get_charset(File file) {
		String charset = "GBK";
		byte[] first3Bytes = new byte[3];
		BufferedInputStream bis = null;
		try {
			bis = new BufferedInputStream(
					new FileInputStream(file));
			boolean checked = false;
			bis.mark(0);
			int read = bis.read(first3Bytes, 0, 3);
			if (read == -1)
				return charset;
			if (first3Bytes[0] == (byte) 0xFF && first3Bytes[1] == (byte) 0xFE) {
				charset = "UTF-16LE";
				checked = true;
			} else if (first3Bytes[0] == (byte) 0xFE
					&& first3Bytes[1] == (byte) 0xFF) {
				charset = "UTF-16BE";
				checked = true;
			} else if (first3Bytes[0] == (byte) 0xEF
					&& first3Bytes[1] == (byte) 0xBB
					&& first3Bytes[2] == (byte) 0xBF) {
				charset = "UTF-8";
				checked = true;
			}
			bis.reset();
			if (!checked) {
				// int len = 0;
				int loc = 0;

				while ((read = bis.read()) != -1) {
					loc++;
					if (read >= 0xF0)
						break;
					if (0x80 <= read && read <= 0xBF) // 单独出现BF以下的，也算是GBK
						break;
					if (0xC0 <= read && read <= 0xDF) {
						read = bis.read();
						if (0x80 <= read && read <= 0xBF) // 双字节 (0xC0 - 0xDF)
															// (0x80
															// - 0xBF),也可能在GB编码内
							continue;
						else
							break;
					} else if (0xE0 <= read && read <= 0xEF) {// 也有可能出错，但是几率较小
						read = bis.read();
						if (0x80 <= read && read <= 0xBF) {
							read = bis.read();
							if (0x80 <= read && read <= 0xBF) {
								charset = "UTF-8";
								break;
							} else
								break;
						} else
							break;
					}
				}
				// System.out.println( loc + " " + Integer.toHexString( read )
				// );
			}

		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			if(bis!=null) {
				try {
					bis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

		return charset;
	}
}
